The present invention is directed to an improved electrically heated ceramic kiln, and more particularly, to a ventilation system for an electrically heated ceramic kiln.
As is well recognized in the art, when firing an electrically heated ceramic kiln, it is necessary to provide adequate ventilation of the interior of the kiln to permit oxidation of the organic material normally present in glazes, bodies, and decorations when the wares are being fired. In addition, ventilation is also needed to remove CO.sub.2, H.sub.2 O and other gases that are released from many of the materials during the firing process. If ventilation is inadequate, physical defects in the wares and glazes usually result. Many colors are also permanently and adversely altered by inadequate ventilation.
Electrically heated ceramic hobby kilns are typically ventilated by removing peep hole plugs which open apertures formed in the top or side walls of the kiln, and by opening lids or doors during the early stages of firing. At some point, the doors or lids are closed and one or two peep holes are left open to ventilate the kiln. When ventilation is provided in this manner, the fumes and gases that are produced in the kiln are discharged into the workroom surrounding the kiln. Because these gases may be unpleasant, and may even contain toxic components such as carbon monoxide from incomplete oxidation, ventilation of the workroom is required. In addition, because ventilation of the kiln is dependent upon natural drafts created by the heating of air within the kiln, the rising hot air and incoming cooler room air causes the kiln to be cooler at the bottom and hotter at the top.
More complex ventilation systems are typically used in commercial kilns. For example, in U.S. Pat. No. 4,291,471 issued to Bloom, a ventilation system is disclosed for venting the pre-heat section of a tunnel kiln. Bloom discloses a kiln having a longitudinal duct and an input tube. Compressed air passes through the input tube and is expelled laterally and vertically to create a turbulent air flow laterally across the pre-heat section of the kiln. This air, which mixes with the contaminated kiln gases, is captured by cones disposed about apertures in the longitudinal duct on the other side of the pre-heat section, and is drawn into the duct. A blower, attached to one end of the duct, vents air from the duct thereby creating a partial vacuum in the duct which draws the contaminant laden air into the duct through the cones. Air curtains prevent outside atmosphere from entering the pre-heat section at either the entrance or the exit. Such a ventilation system, however, does not create downdraft turbulence and suffers from the same lack of temperature uniformity present in the naturally ventilated kilns described above.